Regenerator heat exchange devices or regenerators are well known. One type of regenerator is the rotary air-to-air heat exchanger, which is typically in the form of a rotary heat exchange wheel including a matrix of heat exchange material. For example, see Canadian Patent No. 1,200,237 (Hoagland) and U.S. Pat. Nos. 4,432,409 (Steele) and 4,875,520 (Steele et al.), all assigned to the present assignee (and hereinafter the U.S. Patents being referred to as the '409 and '520 Patents, respectively) and incorporated herein by reference. Rotary air-to-air heat exchangers transfer sensible heat and moisture, usually between ducted and counterflowing airstreams, for the purpose of conserving energy within a building, while providing outdoor air ventilation to remove air pollutants from buildings. For example, heat and moisture from indoor air being exhausted to the outdoors during the heating season are transferred to the cooler, dryer incoming fresh air, and during the cooling season, heat and moisture from entering warm moist outdoor air is transferred to the cooler drier air as it is exhausted to the outdoors. Transfer of heat and moisture in this manner can typically reduce the amount of energy required to heat, cool, humidify or dehumidify the incoming ventilation air typically anywhere between about 50% and about 85%, depending primarily on the performance characteristics of the rotary energy transfer wheel.
It is well known to make such rotary heat exchange wheels with a matrix of heat exchange material (capable of absorbing sensible heat) coated with a desiccant material (capable of absorbing moisture and thus latent as well as sensible heat). Such regenerators are used in heating and/or air conditioning systems in which the transfer of both sensible and latent heat is desired in the ventilation portion of such systems, as, for example, in the case of air conditioning systems used in summer climates characterized by hot and humid outdoor air. In such climates, it is often desirable to bring fresh air in from the outdoors. In this case the regenerators are used to transfer sensible and latent heat from incoming air to the outgoing air. The removal of latent heat from incoming air prior to passing the air over evaporation coils of an air conditioning system helps reduce the heat load imposed on the air conditioning system.
To achieve maximum latent heat transfer, as is well known in the prior art, a suitable sensible heat exchange matrix material such as plastic (i.e., high molecular weight, synthetic polymers), aluminum, or Kraft or other fibrous paper is completely and uniformly coated with a desiccant material in accordance with processes known to those skilled in the art. In one type of regenerator, the matrix comprises a plastic strip coated with a desiccant material wound around a hub so as to form a heat exchange wheel. The airflow through the wheel, and the efficiency of heat transfer by the wheel matrix, are determined in part by the spacing between opposing surfaces of adjacent portions of the strips of the matrix. This spacing can be controlled by controlling the height of embossments in the strip. For a given air flow, the tighter the spacing (or the denser the wrap), the higher the efficiency of heat exchange matrix and the greater the pressure drop across the two sides of the wheel. See U.S. Pat. Nos. 4,432,409 to Steele and 4,825,936 to Hoagland et al. Thus, the rated air flow and efficiency through a regenerator wheel of a given diameter are performance characteristics of the regenerator matrix that are in part determined by the wrap density of the strips.
Minimum amounts of outdoor air ventilation for control of indoor air pollution are now frequently specified by ventilation building codes and standards in terms of cubic feet of air per minute/per occupant (CFM per person), but for a particular space this number may typically vary by a factor of up to four based upon the nature of the occupancy and the anticipated occupant density, e.g., schools, office buildings, libraries, restaurants, etc. Typically, ventilation systems are designed and installed in buildings to meet the initial intended occupancy requirements. For reasons of economy, ventilation systems will also generally be manufactured and installed to only provide minimum required ventilation rates to a building. Such systems may include variable speed blowers and adjustable air dampers to allow for changes of ventilation air in the event of a change of occupancy that requires higher ventilation rates. For ventilation systems including porous heat exchange, energy transfer regenerator wheels, the amount of additional ventilation that can be provided in this manner is, however, partly restricted by the pressure drop across the wheel through which supply and exhaust air must flow. With the pressure drop across the energy transfer wheel increasing in direct proportion to the increase of airflow, the maximum pumping capacity of a variable speed blower can be reached before the desired increase of airflow is obtained.
Further, under some circumstances maximum latent heat transfer may not be desirable. For example, under moderate winter conditions it is often desired to use a ventilation system including a sensible heat exchange matrix wheel to remove substantial amounts of moisture from a building. However, when the outdoor air becomes very cold and dry the moisture removal rate provided by a sensible heat exchange matrix wheel may become excessive, and the indoor air humidity may become uncomfortably low. In this case it becomes desirable to have some desiccant coating present on the heat exchange matrix so as to increase moisture retention (and thus allow additional moisture in the air being exhausted from the building to be transferred to the incoming fresh air), but a fully desiccant coated wheel may retain excessive amounts of moisture so that an excessive amount of moisture is returned to the interior of the building with the incoming fresh air.
Such moisture control problems, thus, are not necessarily solved by substituting a latent heat exchange matrix wheel (i.e., wheels heretofore only available with a matrix having a uniform coating of desiccant material) for a sensible heat exchange matrix wheel (i.e., a wheel having a matrix made entirely of sensible heat exchange materials). Whereas a fully desiccant-coated matrix wheel may retain excessive amounts of moisture, a sensible matrix wheel without a desiccant coating material recovers only moisture which condenses on the matrix when the dew point of the airstream is above the temperature of the surface of the matrix. The condensed moisture is reevaporated back into the warmer and drier counterflowing airstream passing through the matrix. This small amount of moisture recovery by a sensible heat exchange matrix may be insufficient to maintain the desired indoor humidity.
The latent heat exchange efficiency desired of a heat exchange matrix also may vary according to changes in the usage of the building it services. For example, the moisture removal rates desired in a retail space may differ from that desired in the same space later converted to a restaurant. Furthermore, in some situations, the desired latent heat exchange efficiency may not be fully determinable until the regenerator is tested at the building itself. Under such circumstances, it is possible that neither regenerators made entirely of heat exchange materials uniformly coated with desiccant material, nor regenerators made entirely of sensible heat exchange materials (not coated with desiccant material) provides the desired latent heat exchange efficiencies since regenerators of both types are usually offered in only a limited number of values of efficiency.
Moreover, after the system is installed the volumetric air flow requirements may change, because of a change of use or occupancy. More specifically, ventilation systems are usually designed to provide a predetermined volumetric air flow so as to meet specific building code and use requirements. If the system including the blower and heat regenerator wheel are originally designed for one range of air flows, and the changes require a different range of air flows, adjustments must be made. Typically, due to the costs of installing ventilation systems in large buildings, such changes in the ventilation system after they are installed are not readily accomplished. For example, the volumetric rate of air flow can be adjusted by only a small amount by changing the pulley systems of the blower. One could also change the entire regenerator matrix wheel with one of a different wrap density. Thus, following installation of a ventilation system, it may be necessary to adjust the flow rate and/or other performance characteristics of the regenerator matrix wheels in response to changes in building design or usage.
Thus, it would be advantageous to be able to customize or adjust in an economical way the airflow rates, customize or adjust the latent and sensible heat transfer characteristics of the regenerator wheel, or customize or adjust some other performance characteristic during or after its manufacture or at the installed site.